Catalytic reactor for endothermic reactions

ABSTRACT

A catalytic reactor for endothermic reactions, having a catalyst located in a housing which is formed of refractory material, and at least one tubular catalytic vessel arranged in the interior of the housing. A plurality of catalytic vessels are arranged at a distance from one another in the housing, and a plurality of burners are arranged in the housing in such a way that the catalytic vessels lie between the burners. The flame region of the burners lies in the region of the heat distributors in each instance so as to ensure non-adiabatic combustion.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention is directed to a catalytic reactor. For endothermicreactions. Examples of such reactions are the production of hydrogen bysteam reformation of hydrocarbons and dehydrogenation processes that arecarried out, e.g., for the production of styrene from ethylbenzene or ofpropylene from isobutane.

2. Description of the Prior Art

A catalytic reactor having an external cylindrical shape and a reactionchamber with a circular cross section is known from EP 0 380 192 B1. Theinput material to be catalyzed is introduced from the bottom into thereaction chamber which is filled with a catalytic material, while theobtained catalytically converted product is extracted from the upper endof the reaction chamber. This known reactor is heatable by means of aburner which is arranged below the base level of the reaction chamberand enclosed in the region of its combustion zone by a refractory shell.The flame direction of the burner is oriented coaxially to thelongitudinal direction of the reaction chamber. The ascending combustiongases of the burner are guided along virtually the entire length of thereaction chamber in a heat distributor which is formed as a tubular bodyfrom a material with good heat conduction and directly adjoins therefractory combustion chamber wall. An annular gap remains open betweenthe tubular heat distributor and the inner defining wall of the annularreaction chamber. The occurring hot combustion gases are therefore firstguided upward by the heat distributor and are deflected into the annulargap at the upper end of the heat distributor. The combustion gases thenflow downward through the annular gap and, in so doing, give off heatinto the reaction space through the inner defining wall. At the sametime, however, the combustion gases flowing downward past the wall ofthe heat distributor also absorb heat from the hot combustion gasesflowing upward in the interior of the heat distributor so that thetemperature of the gases in the annular gap remains virtually constant.In this way, the known device can be operated as an isothermal reactorin practice.

In another embodiment form, the reactor known from EP 0 380 192 B1 has aplurality of parallel heat distributors arranged in place of a centralheat distributor. There is also only one burner provided in this device,this burner being arranged with its combustion space below the baselevel of the reaction chamber. Since practically no heat is given offexternally in the combustion space itself, the combustion of the fuelused in each case takes place under adiabatic conditions so that,depending on the fuel, undesirably high flame temperatures are reached.In order to decrease the temperature of the combustion gases, theconventional amount of approximately 10% excess air can be considerablyincreased, e.g., to 50%. However, this leads to a compulsorycorresponding increase in the amount of exhaust gas with the consequentheat losses, which is also undesirable. As an alternative to a reductionin temperature, EP 0 380 192 B1 proposes a return of exhaust gas to thecombustion zone. This has the particular disadvantage of additionalconstruction costs.

Another endothermic reactor is known from EP 0 369 556 B1. The reactionchamber of this reactor, which is filled with a catalyst, is designed asa tubular shell or sheathing tube which is closed at the bottom end. Anascending pipe is inserted into the latter in such a way that thematerial to be processed can flow in opposite directions through theannular space between the sheathing pipe and the ascending pipe, on theone hand, and through the ascending pipe, on the other hand, in order topass the reaction space. In this apparatus, the hot combustion gas forheating the reaction space is generated in a separate part of theinstallation under adiabatic conditions and is subsequently introducedlaterally into the refractory housing in the lower end region of thereaction space, this housing enclosing the reactor externally at adistance. In order to prevent hot combustion gas from striking the wallof the reaction space directly and causing damage as a result of thehigh temperature, the combustion gas is fed in the housing in such a waythat the hot gases first strike a tubular barrier of refractorymaterial, are deflected upward, and guided down again from the upper endof the refractory barrier along a second tubular barrier formed of amaterial with good heat conducting properties. The combustion gas canonly flow up again at the bottom end of the second barrier and come intoa heat-exchanging contact with the wall of the reaction space. At thesame time, heat transfer takes place between the combustion gasesflowing in opposite directions through the heat conducting wall of thesecond barrier. As in the device known from EP 0 380 192 B1, these stepsbring about an appreciable reduction in the temperature of thecombustion gas so that the wall of the reaction chamber is protectedfrom impermissible thermal loading. The reaction space of this reactoris limited to a single reactor vessel so that the reactor vessels ininstallations having different output capacities must be provided withnew dimensions as appropriate. Further, it is disadvantageous that thebarriers which are exposed to high temperatures have closing or sealingparts which must be exchanged after a certain period of operation.

SUMMARY OF THE INVENTION

The object of the present invention is to improve a catalytic reactorfor endothermic reactions of the type mentioned above so that thereactor vessel is protected against thermal damage without the drawbacksof costly construction steps, unwanted increases in exhaust gasquantities or disadvantages in the utilization of energy of the fuelsemployed.

Pursuant to this object, one aspect of the present invention resides ina catalytic reactor having a housing formed of a refractory material anddefining an interior that is heatable by hot combustion gases. A fluegas outlet line is connected to the housing to guide the combustiongases therefrom. A plurality of tubular catalytic vessels are arrangedat a distance from one another within the interior of the housing and acatalytic material is arranged within the catalytic vessels. A processgas feed line is connected to the catalytic vessels to feed in materialwhich is to be catalytically processed. A product gas outlet line isconnected to the catalytic vessels to guide out a product formed bycatalytic reaction of the fed in material. A plurality of tubular heatdistributors are provided so that one of the heat distributors isassigned to each catalytic vessel and encloses the catalytic vessel overat least a portion of its axial length so as to form a narrow annulargap between the heat distributor and catalytic vessel. The narrowing orgap forms a passage for the hot combustion gases. Additionally, aplurality of burners are arranged in the housing so that the catalyticvessels are situated between the burners. Each of the burners has aflame region in the vicinity of the heat distributors so as to ensurenon-adiabatic combustion.

In another embodiment of the invention the catalytic vessels arearranged vertically and substantially parallel to one another so thatdirectly adjacent catalytic vessels are spaced equidistantly.Furthermore, the burners are arranged symmetrically with respect to thecatalytic vessels.

Still another embodiment of the invention provides the catalytic vesselsto be arranged so that longitudinal axes thereof lie in a common plane.The burners are arranged adjacent to one another in two rows in amirror-symmetrical manner with respect to the plane of the longitudinalaxes of the catalytic vessels.

Yet another embodiment of the invention provides the burners arranged tohave a vertical flame direction, preferably downwardly directed.

In an additional embodiment of the invention the catalytic vessels aresealed at their bottom end by a base. An ascending pipe is provided foreach catalytic vessel and is arranged within the vessel coaxially to thelongitudinal axis of the vessel and substantially along the entirelength of the vessel so as to end at a slight distance from the base toform a through-gap. The ascending pipe forms an annular space betweenthe ascending pipe and the outer wall of the catalytic vessel. Thecatalytic material is arranged within the annular space.

In a further embodiment of the invention the catalytic vessels and theheat distributors are connected to an upper part of the housing so as tobe freely suspended so that lower ends of the catalytic vessels and heatdistributors are at a distance from the bottom of the housing so thatlongitudinal thermal expansion can take place while maintaining theentrance gap for the combustion gases open.

The essential aspect of the invention consists is in that the combustionis carried out under nonadiabatic conditions, that is, heat is alreadyguided out of the flame zone during combustion so that the maximum flametemperature which occurs is substantially decreased. This is achieved byproviding not only a plurality of burners, but also a plurality ofcatalytic vessels which penetrate into the flame space of the burners.The catalytic vessels are enclosed within the region of the flame spacein each instance by a barrier which will be referred to hereinafter as aheat distributor, since it is formed of a material with good heatconduction and absorbs the heat and distributes it again in the mostuniform manner possible. The catalytic vessels are arranged between theburners, respectively.

The invention is explained more fully in the following with reference tothe embodiment examples shown in the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a longitudinal section through a reactor according to theinvention;

FIG. 1a shows detail X in FIG. 1;

FIG. 2 shows a cross section along the line A--A in FIG. 1;

FIG. 3 shows cross section along the line B--B in FIG. 1;

FIG. 4 shows a longitudinal section of a modified reactor;

FIG. 4a shows an enlarged view of the bottom end of the reactor vesselin FIG. 4;

FIG. 5 shows a longitudinal section through an isothermal reactoraccording to the invention;

FIG. 6 shows cross section along the line C--C in FIG. 5; and

FIG. 7 shows an enlarged detail section of the reactor in FIG. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the catalytic reactor which is shown in different sections in FIGS. 1to 3, a total of five tubular catalytic vessels 10 are arranged parallelto one another in the vertical longitudinal direction. Theirlongitudinal axes lie in a common plane H. The catalytic vessels 10 arepreferably equidistant with respect to the directly adjacent catalyticvessels 10 (FIG. 3). A row of four burners 15 is arranged, in eachinstance, on both sides of the plane H at a distance from the catalyticvessels 10, these burners 15 being spaced from one another in the sameway as the catalytic vessels 10. The longitudinal axes of the burners 15are offset with respect to the longitudinal axes of the catalyticvessels 10 so that the burners 15 of the two rows of burners areadvantageously located opposite one another in the region of theintermediate space adjacent catalytic vessels 10.

Arrangements of burners 15 and catalytic vessels 10 other than themirror-symmetrical arrangement can also be selected. For example, therows of burners can be positioned concentrically in and around acircular arrangement of the catalytic vessels 10, which would alsoresult in a symmetrical arrangement. A less uniformly ordereddistribution of the burners 15 and catalytic vessels 10 would also bepossible in principle. However, the symmetrical arrangement hasconsiderable advantages with regard to the most uniform possible thermaleffect.

The burners are preferably oriented vertically with respect to theirflame direction, specifically so as to be directed from top to bottom.It would also be possible in principle to arrange the burners diagonallyto the longitudinal axis of the catalytic vessels 10 or even at rightangles from the side thereof, although the parallel arrangement ispreferable because of the more uniform temperature distribution. In afurther embodiment of the invention, a plurality of rows of catalyticvessels 10 arranged parallel to one another so as to alternate with therows of burners could also be provided instead of a single row. In thisway, it is possible to adapt to the required reactor capacity invirtually any manner desired without having to alter the construction ofthe individual catalytic vessels 10.

As is shown by the longitudinal section in FIG. 1, the reactor accordingto the invention, which is shown by way of example, has a housing 13which is formed of refractory material. The lower portion of the housing13 widens to form a radiation chamber 14 which receives the burners 15in wall openings in its roof The catalytic vessels 10, only one of whichis shown in longitudinal section, penetrate into the radiation chamber14 from above by approximately one third of their length. Everycatalytic vessel 10 has a product gas feed line 17 for the inputmaterial which is to be catalytically converted. In this example, theproduct gas feed line 17 is arranged laterally at the upper end of thehousing 13. Since an ascending pipe 18 which extends practically alongthe entire axial length of the catalytic vessel 10 is installedconcentrically in the catalytic vessel 10 in each instance, the productgas outlet line 19 through which the products generated in the catalyticreaction are removed can likewise be arranged laterally in the upperpart of the catalytic vessel 10. This has the advantage that each of thecatalytic vessels 10 can be fitted at their upper end in the housing 13so as to be freely suspended. Since a sufficiently large distance isallowed for between the bottom end of the catalytic vessel 10 and thebase of the housing 13 in the nonoperational state, the catalyticvessels 10 can expand freely downward in the operating state whenheated. If the product gas outlet line 19 were to be connected to theend of the catalytic vessel 10 located opposite the process gas feedline 17, costly design steps would have to be undertaken to compensatefor thermal expansion so as to prevent damage to the pipelines.

Since the process gas feed line 17 and the product gas outlet line 19are not arranged at the extreme upper end of the catalytic vessel 10,but rather slightly below it, the upper end face could be provided withan easily accessible, removable cover 12 through which the catalyticmaterial can be introduced and exchanged when required. The catalyticvessels 10 are enclosed along their entire length penetrating into theradiation chamber 14 by a tubular heat distributor 16 which is formed ofa material with good heat conducting properties, preferably aheat-resistant steel, so that an annular gap 21 is formed between thewall of the catalytic vessel 10 and the heat distributor 16. This isshown more clearly in FIG. 1a, which shows a detailed enlargement ofdetail X from FIG. 1. It can be seen that the catalytic vessel 10 istightly closed at its lower end side by a base. The product gas flowingdownward through the catalytic mass 10a located in the annular chamber11 is deflected in the region of the end side and can flow through anannular through-gap into the ascending pipe 18 and can be extracted atthe top. This gap passage is formed in that the ascending pipe 18 endsat a short distance from the base of the catalytic vessel 10. Theproduct gas outlet line 19 is connected with the ascending pipe 18(FIG. 1) and guided out through the wall of the catalytic vessel 10. Thetubular heat distributors 16 are fitted to the roof of the radiationchamber 14. The length of the heat distributors 16 is so dimensionedthat a sufficiently large distance is maintained between the base of thehousing 13 and the end side of the heat distributor 16 while taking intoaccount the thermal longitudinal expansion during operation, so that thehot combustion gas can flow upward into the annular gap 21 between theheat distributor 16 and the catalytic vessel 10 via the entrance gap 20.In many cases, it is advisable to provide slots in the wall of the heatdistributors 16 so that the combustion gases can enter the gap 21. Thishas the advantage that the flow conditions of the combustion gases canbe adjusted in a directed manner exclusively by the selection of thequantity and dimensions of these slots without having to change theexternal geometry of the heat distributors 16 and catalytic vessels 10.

The heat needed for the endothermic reaction is fed to the process gasflowing through the catalytic vessel 10 from the partial flow of thecombustion gases entering through the gap 21. However, since the heatdistributor 16 conducts heat, this combustion gas flow, at the same timethat it gives off its heat, absorbs heat again from the radiationchamber 14 through the wall of the heat distributor 16 so that itretains virtually the same temperature until reaching the height of theroof of the radiation chamber 14. But this temperature liessubstantially below the adiabatic flame temperature, since heat isconstantly given off to the process gas for the endothermic catalyticreaction during combustion.

Above the roof of the radiation chamber 14, the catalytic vessels 10 areenclosed at a slight distance by the refractory material of the housing13 similarly to the manner in which they are enclosed by the heatdistributor 16 so that the gap 21 is continued upward. Of course, itwould also be possible to continue the heat distributors 16 until theupper end of the housing 13 and to arrange the housing wall only aroundthe upper portion of the heat distributors. In the upper portion of thecatalytic vessel 10, i.e., along approximately 2/3 of its length in theexample shown in FIG. 1, the temperature of the combustion gases dropscontinuously due to the constant delivery of heat and the absence of anypossibility of absorbing heat. The cooled combustion gas leaves thereactor through the flue gas outlet line 22 and can be reused in aconvection portion of a more complex overall installation, not shown.

FIGS. 4 and 4a show a modified embodiment form of the reactor accordingto the invention. Parts performing functions identical to those shown inFIGS. 1 to 3 are provided with the same reference numbers and need notbe discussed again. In contrast to the first embodiment example, thisreactor has a helical baffle 24 within the annular gap 21, this baffle24 displacing the through-flowing combustion gas flow in an additionalrotational movement about the longitudinal axis of the distribution isachieved in a particularly uniform temperature distribution is achievedin the heating of the reactor due to the helical overall movement of thecombustion gas flow which is brought about in this way.

The lower end of the catalytic vessel 10 with the heat distributor 16 isshown as an enlarged detail in FIG. 4a. As in FIG. 4, an installation,which acts as a heat exchange promoter 23 and is constructed in the formof a preferably tubular flow displacement body which extends coaxiallysubstantially over the entire length of the ascending pipe 18, isarranged in the ascending pipe 18. The outer diameter of the heatexchange promoter 23 is smaller than the inner diameter of the ascendingpipe 18 so that an annular space 25 is formed between the two diameters.The tubular body of the heat exchange promoter 23 is tightly sealed onthe inside (e.g., in the lower portion) so that the product gas formedby catalysis can only flow up through this annular space 25 to theproduct gas outlet line 19 after leaving the annular chamber 11 which isfilled with the catalytic material. In this way, the product gas iscompelled to an intimate heat exchange with the downward flowing processgas to be heated, which is effected through the wall of the ascendingpipe 18. Of course, a flow displacement body formed of solid materialcould also be used instead of a tubular heat exchange promoter 23.

FIGS. 5 to 7 show another embodiment of the invention, the constructionof the housing 13 and the arrangement of the burners 15 and catalyticvessels 10 being shown schematically in FIGS. 5 and 6, while FIG. 7shows a more detailed view of the catalytic vessel 10. Again, partshaving the same function are provided with identical reference numbers.This embodiment differs from the first embodiment in that the radiationchamber 14 practically occupies the entire housing 13 and the heatdistributors 16 extend in each instance substantially along the entireaxial length of the catalytic vessels 10. In this way, the combustiongas flowing upward through the gap 21 can give off heat to the processgas along its entire path and can absorb heat at the same time throughthe wall of the heat distributor 16 so that its temperature ismaintained practically constant along this path. An isothermal catalyticreactor is formed in this way. Consequently, the product gas flowingupward through the ascending pipe 18 has the same temperature as theprocess gas flowing downward through the annular space 11 so that thereis no transfer of heat between these two gas flows. The installation ofa flow displacement body in the ascending pipe can therefore be omitted.

A particular advantage of the invention consists in that the output of acatalytic reactor can be changed within wide limits in the planningstage simply as a result of the quantity of catalytic vessels 10 andburners 15 without changing the individual catalytic vessels 10. As aresult of the nonadiabatic combustion, the flame temperatures areappreciably reduced so that no complicated and accordingly expensiverefractory constructions are required. Further, the thermal loading ofthe tubular heat distributor remains comparatively low.

A construction corresponding to the embodiment forms in FIGS. 1 to 4 issuitable particularly for the steam reformation of hydrocarbons, whilean isothermal reactor such as that shown in FIGS. 5 to 7, isadvantageous particularly for dehydrogenation processes such as thosementioned previously.

What is claimed is:
 1. A catalytic reactor for endothermic reactions,comprising:a housing formed of refractory material and defining aninterior that is heatable by combustion gases; a flue gas outlet lineconnected to the housing to guide out the combustion gases; a pluralityof tubular catalytic vessels arranged at a distance from one another inthe interior of the housing, the catalytic vessels having a bottom endthat is sealed by a base, and further comprising, for each catalyticvessel, an ascending pipe arranged within the vessel coaxial to thelongitudinal axis of the vessel and substantially along the entire axiallength of the vessel so as to end at a distance from the base to form athrough-gap and so as to form an annular space between the ascendingpipe and an outer wall of the catalytic vessel, a catalytic materialbeing arranged within the annular space; a process gas feed lineconnected to the catalytic vessels to feed in material to becatalytically processed; a product gas outlet line connected to a topend of the ascending pipe for guiding out a product formed by catalyticreaction; a plurality of tubular heat distributors, each of the tubularheat distributors being respectively arranged to enclose one of thecatalytic vessels over at least a portion of its axial length so as toform an annular gap between the respective heat distributor andcatalytic vessel which allows passage of the combustion gases; and aplurality of burners arranged in the housing so that the catalyticvessels are situated between the burners, the burners having a flameregion in the vicinity of the heat distributors so as to ensurenon-adiabatic combustion.
 2. A reactor according to claim 1, wherein thecatalytic vessels are arranged vertically and substantially parallel toone another so that directly adjacent catalytic vessels are spacedequidistantly, the burners being arranged symmetrically with respect tothe catalytic vessels.
 3. A reactor according to claim 2, wherein atleast some of the catalytic vessel are arranged so that longitudinalaxes thereof lie in a common plane, the burners associated with thealigned catalytic vessels being arranged adjacent to one another in tworows in a mirror-symmetrical manner with respect to the plane of thelongitudinal axes of the catalytic vessels.
 4. A rector according toclaim 2, wherein the burners are arranged to have a vertical flamedirection.
 5. A reactor according to claim 4, wherein the burners areconfigured to have a downwardly directed flame direction.
 6. A reactoraccording to claim 3, wherein the catalytic vessels and burners arearranged alternately in a plurality of parallel adjacent rows.
 7. Areactor according to claim 3, wherein the burners associated with a rowof catalytic vessels are arranged so that longitudinal axes of theburners are offset with respect to the longitudinal axes of thecatalytic vessels so that a burner of a first row of burners isrespectively located opposite a burner of a second row of burners in anintermediate space formed between adjacent catalytic vessels.
 8. Areactor according to claim 1, wherein the heat distributors areconfigured and arranged to extend substantially along the entire axiallength of the catalytic vessels so as to form an isothermal reactor. 9.A reactor according to claim 1, wherein the heat distributors extendover only a lower portion of the catalytic vessels, the housing beingconfigured to enclose the catalytic vessels along a remaining portion oftheir axial length and to form a continuation of the annular gap.
 10. Areactor according to claim 1, and further comprising a helical bafflearranged in the annular gap so as to displace the combustion gas flowingthrough the annular gap into a helical flow pattern that rotatesexternally about the respective catalytic vessel.
 11. A reactoraccording to claim 1, and further comprising a heat exchange promotorarranged in the ascending pipe to extend coaxially substantially alongthe entire length of the ascending pipe so as to form a second annularspace between the heat exchange promotor and the ascending pipe, throughwhich second annular space the product gas flows upwardly.
 12. A reactoraccording to claim 11, wherein the heat exchange promotor is a tubularflow displacement body.
 13. A reactor according to claim 1, and furthercomprising a cover arranged in an upper end of each catalytic vessel,the cover being configured to permit introduction of the catalyticmaterial into the catalytic vessel, the process gas feedline and theproduct gas outlet line being arranged to extend laterally from an upperportion of the catalytic vessel below the cover.
 14. A reactor accordingto claim 1, wherein the housing has a bottom, the catalytic vessels andthe heat distributors being connected to an upper part of the housing soas to be freely suspended so that lower ends of the catalytic vesselsand heat distributors are at a distance from the bottom of the housingand so that a free suspension is insured which allows for thermallongitudinal expansion during operation and so that an entrance gapformed between each of the heat distributors and the respectivecatalytic vessel, remains open which permits the combustion gases toflow into the annular gap.
 15. A reactor according to claim 1, whereineach of the heat distributors has a wall with a slotted lower end whichpermits the combustion gases to enter into the annular gap.